> (average debt of a student now is around £18K. I estimate this to increase to about £24K)

I think the increase will be more than that. Tuition fees are due to rise from the current £3000 to a maximum of £9000 pa. This is on top of a loan for living expenses of £4000. So a typical student debt may rise to £39k. Furthermore the government is increasing the interest rates on loans.

All this together will make a well-paying job more attractive to a programmer having just left university than a startup.